The present invention relates to a process for preparing a colorless and odorless rosin ester having a higher thermal stability and weatherability.
Heretofore, rosin esters have been used as tackifiers for hot-melt adhesives and pressure-sensitive adhesives, modifiers for rubbers and plastics, raw materials for traffic paints, or base materials for chewing gum.
Common rosin esters are colored in yellow or yellowish brown, impart their characteristic odor and are poor in thermal stability and weatherability (hereinafter referred to thermal stability and weatherability as stability). As a rosin ester improved in such properties, disproportionated rosin ester or hydrogenated rosin ester which is prepared from disproportionated rosin or hydrogenated rosin is commercially available. However, these rosin esters also do not have sufficient color, stability, and the like.
Japanese Examined Pat. Publication No. 33771/1970 and Japanese Examined Pat. Publication No. 20599/1974 disclose a method for disproportionating rosins or rosin compounds with a specific organic sulfur compound. However, the disproportionated rosins or rosin compounds do not have sufficient color and stability and impart odor.
Japanese Unexamined Pat. Publication No. 9605/1980 discloses a process for preparing rosin esters having a higher stability, comprising purifying a disproportionated rosin as a starting material to remove high molecular weight materials and unsaponifiable materials and esterifying the purified disproportionated rosin with an alcohol. The obtained rosin ester is relatively superior in stability to conventional rosin esters. However, the obtained rosin ester is colored during esterifying and does not have a sufficient stability for heat discoloration. Accordingly, the obtained rosin ester should be improved upon the properties mentioned above.
Japanese Unexamined Pat. Publication No. 230072/1984 discloses a process for preparing a light-colored rosin ester having a higher stability, comprising esterifying a rosin which is purified by distilling with an alcohol in the presence of a specific organic sulfur compound having abilities of both disproportionating and decoloring. However, the obtained rosin ester does not have sufficient color and stability and there is a problem that the obtained rosin ester is odorous which is generated from an organic sulfur compound when the rosin ester is heated.
As mentioned above, any conventional rosin esters have not yet been satisfactory in odor, color and stability at a time and the rosin esters could not have been competed at all in the above properties with hydrogenated petroleum resins which are employed in the same uses of the rosin esters.
In the course of studying to develop a novel process for preparing a rosin ester having improved properties such as color, odor and stability in comparison with those of conventional rosin esters, the present invention has been accomplished.
The process for preparing a rosin ester having improved properties mentioned above has been investigated with giving a consideration of the orders of a process for purifying a rosin and/or a disproportionated rosin each of which is a starting material (hereinafter referred to as "raw rosin"), a process for hydrogenating the raw rosin and a process for esterifying the raw rosin. As the results, it has been found that a rosin ester which is practically colorless and excellent in various properties such as odor at heating, stability and compatibility can be provided by a process for preparing a rosin ester which comprises purifying and then esterifying a raw rosin and subjecting the resultant to hydrogenating. The present invention has been accomplished in accordance with the above results.
These and other objects of the invention will become apparent from the description hereinafter.